Frictional damping strut

ABSTRACT

The invention comprises a frictional damping strut. The strut comprises an inner cylinder that slides within an outer casing. A spring biases the inner cylinder away from the outer casing in an axial direction. A first wedge member cooperatively engages a second wedge member. The first wedge member having a frictional engagement with the inner cylinder such that when the inner cylinder is pressed into the outer casing the first wedge member bears upon the second wedge member causing the first wedge member to radially expand, thereby increasing a frictional force between the first wedge member and the inner cylinder. A second spring preloads the first wedge member against the second wedge member. A belt tensioner may incorporate the damping strut to preload a belt and damp belt oscillations.

FIELD OF THE INVENTION

[0001] The invention relates to struts, more particularly to frictionaldamping struts that are spring biased and have cooperating wedge membersfor damping a movement.

BACKGROUND OF THE INVENTION

[0002] Shock absorbers and struts and more particularly frictionaldamping struts are used to absorb and damp oscillatory movements in anumber of applications. Applications include vehicles and machinery thatare subject to repetitive oscillatory movements and vibration.Generally, a load is absorbed by a spring means while oscillations areabsorbed and damped by viscous or frictional movement of cooperatingparts.

[0003] Representative of the art is U.S. Pat. No.2,429,140 (1947) toSnyder which discloses a shock absorber having a friction unit actuatedby an expander.

[0004] Also representative of the art is U.S. Pat. No. 4,606,442 (1986)to Paton et al. which discloses an assembly comprising damper shoes thatare guided by and wedged transversely between two wedge rings.

[0005] Frictional damping strut assemblies may be incorporated into atensioner assembly. A tensioner may be used to preload an engine drivebelt in order to maximize operational efficiency and to minimize noiseand vibration during belt operation.

[0006] Representative of the art is U.S. Pat. No. 5,951,423 (1999) toSimpson which discloses a mechanical friction tensioner having springloaded wedge-shaped blocks and friction damping. The tensioner has awedge-shaped piston that interacts with spring biased wedge-shapedblocks. As the piston moves inward the wedge-shaped blocks are pushedoutward to provide friction damping.

[0007] The prior art damping struts are relatively complex and do notafford asymmetric damping.

[0008] What is needed is a damping strut having cooperating simplifiedwedge members. What is needed is a damping strut having a simplifiedwedge member providing proportional frictional damping. What is neededis a damping strut providing asymmetric damping. What is needed is atensioner having a damping strut having a simplified wedge member. Thepresent invention meets these needs.

SUMMARY OF THE INVENTION

[0009] The primary aspect of the invention is to provide a damping struthaving cooperating simplified wedge members.

[0010] Another aspect of the invention is to provide a damping struthaving a simplified wedge member providing proportional frictionaldamping.

[0011] Another aspect of the invention is to provide a damping strutproviding asymmetric damping.

[0012] Another aspect of the invention is to provide a tensioner havinga damping strut having a simplified wedge member.

[0013] Other aspects of the invention will be pointed out or madeobvious by the following description of the invention and theaccompanying drawings.

[0014] The invention comprises a frictional damping strut. The strutcomprises an inner cylinder that slides within an outer casing. A springbiases the inner cylinder away from the outer casing in an axialdirection. A first wedge member cooperatively engages a second wedgemember. The first wedge member having a frictional engagement with theinner cylinder such that when the inner cylinder is pressed into theouter casing the first wedge member bears upon the second wedge membercausing the first wedge member to radially expand, thereby increasing africtional force between the first wedge member and the inner cylinder.A second spring preloads the first wedge member against the second wedgemember. A belt tensioner may incorporate the damping strut to preload abelt and damp belt oscillations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated in and form apart of the specification, illustrate preferred embodiments of thepresent invention, and together with a description, serve to explain theprinciples of the invention.

[0016]FIG. 1 is a cross-sectional view of the inventive strut.

[0017]FIG. 2 is a cross-sectional exploded view of the inventive strut.

[0018]FIG. 3 depicts a plan view of the inventive strut in use on a belttensioner.

[0019]FIG. 4 is a plan view of the first wedge member.

[0020]FIG. 5 is a cross-sectional view of the first wedge member at 5-5in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021]FIG. 1 is a cross-sectional view of the inventive strut. Strut 200comprises cylindrical outer casing 201. Liner 206 lines an inner surfaceof outer casing 201. Liner 206 has a predetermined coefficient offriction which may be varied to increase or decrease a frictional force.Inner cylinder 208 is slideably engaged with liner 206. Cylinder 208moves longitudinally along axis A-A within liner 206 and therebycoaxially within outer casing 201.

[0022] Cylinder 208 bears upon first biasing member or spring 202 whichurges cylinder 208 axially away from outer casing 201 along axis A-A.Spring 202 has a spring rate, k. Spring rate k is selected to assureproper operation based upon a load L imposed on the strut duringoperation.

[0023] Tube 210 is attached to and extends coaxially within outer casing201, while having sufficient radial clearance to allow placement ofspring 202 between tube 210 and liner 206. Second wedge member 204 isformed at an end of tube 210.

[0024] Second biasing member or spring 207 bears upon sliding member 212and wedge member 204. Sliding member 212 is slidingly engaged with aninner surface of tube 210. Rod 211 is fixedly connected to slidingmember 212 thereby constraining spring 207 between sliding member 212and wedge member 204. Spring 207 compresses wedge member 209 between anend 222 of rod 211 and wedge member 204. Rod 211 is slidingly engagedwith a bore through wedge member 204.

[0025] First wedge member 209 also comprises surface 214 whichfrictionally engages cooperating surface 213 in cylinder 208, see FIG. 4and FIG. 5, each a detail of wedge member 209. The pleated form ofsurface 213 and 214 allows a greater normal force to act upon the areathan would otherwise be possible based solely upon a cylindrical ortubular form for surface 213 and surface 214. A frictional force is afunction of, among other things, a surface coefficient of friction, asurface area as well as a normal force acting upon the surface area. Onemay increase a frictional force by increasing a normal force. A normalforce of the inventive strut is greater that of a similarly sized priorart strut by virtue of the angled contact surface realized by a pleatedform for surface 213 and 214. Surface 213 and 214 creates a greaterfrictional force and thereby greater damping force per spring 207 unitoutput, thereby providing an inventive strut having an increased dampingcapability in a smaller physical package. Wedge member 209 alsocomprises frustoconical hole 221. Wedge member 204 cooperatively engageshole 221.

[0026] In operation, in response to a load L, cap 205 and cylinder 208move in direction D1. Movement of cylinder 208 into outer casing 201 indirection D1 is opposed by the biasing action of spring 207 as well asby the frictional engagement of surface 213 with surface 214. Suchfrictional engagement between surface 213 and surface 214 urges wedgemember 209 into pressing engagement with wedge member 204. Due to thefrustoconical shape of wedge member 204 when wedge member 209 is urgedagainst wedge member 204 such action causes wedge member 209 to radiallyexpand. Such expansion of wedge member 209 causes increased normal loadon surface 213 and surface 214 and thereby an increased frictional forcebetween surface 213 and surface 214. Increased frictional force causesincreased resistance to movement of cylinder 208 in direction D1,thereby damping a movement of cylinder D1.

[0027] Movement of cylinder 208 in direction D2 results in a lesserfrictional force being applied by wedge member 209 to cylinder 208. Moreparticularly, wedge member 209 moves slightly in direction D2 whichlessens the force on wedge member 204. However, wedge member 209experiences resistance to further movement in direction D2 becausespring 207 is operating on member 212 which is connected to rod 212which, in turn, restrains a further movement of wedge member 209. Thishas the effect of reducing the normal force on surface 213 which reducesthe frictional force between surface 213 and surface 214. Consequently,movement of cylinder 208 in direction D1 is asymmetric with respect to amovement in direction D2 because in direction D2 it is subject to areduced frictional, and thereby damping, force as compared to directionD1.

[0028]FIG. 2 is a cross-sectional exploded view of the inventive strut.Sliding member 212 is press fit onto or otherwise attached to an end ofrod 211. Spring 207 is constrained between sliding member 212 and wedgemember 204. A force exerted by spring 207 presses wedge member 204against an inner frustoconical surface of wedge member 209. Wedge member204 describes an angle α with respect to an axis A-A.

[0029] Liner 206 engages an inner surface 220 of outer casing 201. Adamping rate of the strut may be adjusted by changing a spring rate K ofspring 207. Increasing a spring rate increases the normal force exertedby wedge member 204 upon wedge member 209, thereby increasing a dampingcoefficient. The converse is also true, i.e., decreasing a spring ratedecreases a normal force exerted by wedge member 204 upon wedge member209, thereby decreasing a damping coefficient. One can also appreciatethat the normal force can be adjusted by changed the angle α, which willdirectly affect a damping rate. Changing angle α will change the extentto which wedge member 209 is expanded against cylinder 208.

[0030] One skilled in the art can appreciate that a spring rate forspring 202 determines the magnitude of a load L that can be borne by thestrut. That is, the magnitude of L for an appropriate application willincrease or decrease with a like change in a spring rate for spring 202.

[0031]FIG. 3 depicts a plan view of the inventive strut in use on a belttensioner. Strut 200 is pivotably connected to an engine block at pivot600 by fitment 231 which is connected to outer casing 201. The other endof strut 200 comprises connector 230, which is attached to cylinder 208.Connector 230 is pivotably attached to a pulley base 400 at pivot 700. Apulley 300 is rotationally attached to base 400. Base 400 is pivotablyconnected to an engine block at pivot 500. Belt B is trained betweenpulleys P1, P2, and P3 on an engine front end accessory drive system.The tensioner maintains a proper predetermined tension in the belt inorder to prevent belt noise and slipping. As described elsewhere in thisspecification, a belt tension and in turn strut load is a function of aspring rate for spring 202. A higher spring rate allows a greater loadto be borne by the strut and tensioner.

[0032]FIG. 4 is a plan view of the first wedge member. Wedge member 209comprises protrusions 251 extending radially in a star pattern, althoughany plan form is acceptable for the purposes of the invention so long assurface 213 and surface 214 have cooperating shapes. Surfaces 214 ofprotrusions 251 engage cooperating surfaces 213 (not shown). Slots 250extend partially axially through the member. Slots 250 allow member 209to partially expand radially outward when a pressure is applied bysecond wedge member 204.

[0033]FIG. 5 is a cross-sectional view of the first wedge member at line5-5 in FIG. 4. Slot 250 is shown extending partially axially throughmember 209. Rod 211 extends through hole 252.

[0034] Although a single form of the invention has been describedherein, it will be obvious to those skilled in the art that variationsmay be made in the construction and relation of parts without departingfrom the spirit and scope of the invention described herein.

we claim:
 1. A strut comprising: a first member; a second member axiallyengaged with the first member; a biasing member engaged between thefirst member and the second member; a first wedge member having an axisand slidingly engaged with the second member; a second wedge memberconnected to the first member and having an axis; a second biasingmember having a first end immovably fixed; a member attached to thefirst wedge member and engaging a second end of the second biasingmember whereby a movement of the first wedge member is acted upon by thesecond biasing member acting upon the member; the second wedge memberaxially engaged with the first wedge member; and the first wedge memberbeing expandable in response to a pressure from the second wedge member.2. The strut as in claim 1, wherein: the first wedge member having afrustoconical hole; and the second wedge member cooperatively engagingthe frustoconical hole.
 3. The strut as in claim 2, wherein: the firstmember and the second member being coaxially engaged.
 4. The strut as inclaim 3, wherein: the first wedge member further comprises an outerfrictional surface having a pleated form; and the second member havingan inner surface having a pleated form for cooperatively engaging thefirst wedge member outer frictional surface.
 5. The strut as in claim 3,wherein: the first wedge member outer frictional surface and the secondmember inner surface each having a coefficient of friction.
 6. The strutas in claim 3, wherein the member further comprises: a rod slidinglyextending through a bore in the second wedge member whereby the secondbiasing member is oppositely placed from the first wedge member relativeto the second wedge member.
 7. A strut comprising: a first cylinder anda second cylinder axially engaged; a first biasing member engaged withthe first cylinder and the second cylinder; a first wedge surfacefrictionally engaged with a surface of the second cylinder, the firstwedge movable with respect to the second cylinder; a second wedge fixedrelative to the first cylinder and engageable with the first wedge, thefirst wedge expandable upon a movement of the first wedge against thesecond wedge, thereby increasing a frictional force between the firstwedge member and the second cylinder.
 9. The strut as in claim 8 furthercomprising: a second biasing member engaged with the first wedge memberwhereby a first movement of the first wedge member is resisted as apressure between the first wedge member and the second wedge member isdiminished.
 10. The strut as in claim 9, wherein: a second movement ofthe first wedge member is assisted by the second biasing member as apressure between the first wedge member and the second wedge member isincreased.
 11. The strut as in claim 10, wherein: the first wedge memberdescribing a frustoconical hole and the second wedge membercooperatively engaging the frustoconical hole.
 12. The strut as in claim11 further comprising: a member attached to the first wedge member andengaging a second end of the second biasing member whereby a movement ofthe first wedge member is acted upon by the second biasing member actingupon the member.
 13. The strut as in claim 12, wherein the memberfurther comprises: a rod slidingly extending through a bore in thesecond wedge member whereby the second biasing member is oppositelyplaced from the first wedge member relative to the second wedge member.14. The strut as in claim 7, wherein the first wedge surface describes apleated form.
 15. The strut as in claim 10 in combination with: a basepivotally mountable to a surface; a pulley having a belt bearingsurface, the pulley rotationally mounted to the base; and a first end ofthe strut pivotally mounted to the base and a second end of the strutpivotally mountable to a surface.
 16. A damper strut comprising: a pairof cooperating wedges biased together and constrained to move coaxially,at least one wedge frictionally engaged with a moveable surface wherebya movement of the moveable surface presses the wedge against the otherwedge, thereby increasing a normal force between the wedge and themoveable surface and resisting a movement of the moveable surface. 17.The damper strut as in claim 16, wherein: a second movement of themoveable surface decreases a normal force between the wedge and themoveable surface.
 18. The damper strut as in claim 17 furthercomprising: the wedge fixed to a base; the base having a surfacefrictionally engaged with the moveable surface.
 19. The damper strut asin claim 18, wherein the base surface and the moveable surface arebiased apart along an axis of movement of the moveable surface.
 20. Thedamper strut as in claims 19, wherein the moveable surface and the basesurface are substantially cylindrical.